Networking basic 1

What is a protocol?
 When a person speaks he/she uses a language. 
 In order to be understood the grammatical rules of the language needs to be adhered to.
 Similar to humans, equipment used for communication too use a set of rules to communicate.
 These are known as “protocols”

Protocol defined
A protocol is a special set of rules that govern how  the components of a communication system 
communicates with each other.

What a protocol does?
 Protocol achieves:
 What is communicated between computers?
 How it is communicated?
 When it is communicated?
 What conformance (bit sequence) between computers?

Usage of Protocols
Protocols are used for communications (passing of messages) between entities in a system
 Must speak the same language
 Entities
 User applications
 E-mail facilities
 Systems
 Computer
 Terminal

 Remote sensor

Key Elements of a Protocol
Syntax (structure of messages)
 Data formats
 Signal levels
Semantics (meanings of messages)
 Control information
 Error handling
Timing (when stations may transmit, etc.)
 Speed matching

 Sequencing

Message Syntax (Organization)
Cannot be freely structured like human sentences
• Rigidly structured
• General Message Organization 
 Primary components
• Data Field (content to be delivered)
• Header (everything before the data field)
• Trailer (everything after the data field)
 Header and trailer are further divided into fields

General Message Organization

Message Semantics (Meaning)

 Only a few message types are allowed because  computers do not have the intelligence to handle open-ended communication
Message Timing Constraints
 When may a process transmit? At any time? Only  when some event happens?
 Turn-taking in conversations
 In client/server computing, server cannot respond  unless it receives a request
Protocol Implementations
 Are building blocks of a network architecture
 Implemented as a layered structure
 Each protocol object (in a layer) has two different  interfaces
 service interface: defines operations on this protocol

 peer-to-peer interface: defines messages exchanged with peer

 Peer Layer Concept
 Entities on each layer communicate with their equivalent on the other side
 Service Concept
 Each layer uses the ‘service’ provided by the next lower layer
 Each layer provides ‘service’ to the next higher layer
 Independence Concept
 Each layer is independent – It carries out its own task  independently of other layers – Implementation of each layer  is independent within the standards – A layer does not care or 

need to know how the next layer does its job
How Standards Govern Communications
 Standardization has been introduced for protocols  because of the complexity issues cropping up as a  result of having no standards (A million dollar issue  when it comes to interconnectivity)
 Standards govern how the exchange of messages  takes place in communications using protocols
 Messages are governed by strict rules because computers are  not intelligent
Protocol standards
Two categories
 De facto - by fact or convention
 invented by commercial organizations (by vendors)
 proprietary, close standards 
De jure- by law or regulation
 officially recognized by a body (international standards agencies)
 Open standards allow competition among vendors (which in turn reduce prices)

Standardization bodies for network protocols
 International Standards Organization (ISO)
  International Telecommunications Union 
 Telecommunication Standards (ITU-T)

 Internet Engineering Task Force (IETF)